I have set up a website with a Joomla template however with Vista it does not look the same as with other operating systems. Also it changes the way it looks from the Joomla site. Any suggestions would be appreciated.

That my friend is a very broad subject, there are ways to make sites look and feel the same to any and all browsers, now depending on which school of thought you subscribe to you should make your site look it's best in the most popular browser, which apart from all the flame wars about which is the best, the facts are clear, the majority of people browsing using IE 7 with a significant minority using Firefox.
Personally I build sites occasionally and when I do I make them 'best' at 800x600 or higher and IE7, with occasional bits of script to keep the Firefox crew happy.
Another thing to consider is that by saying it looks different does that imply 'wrong' or just that, just different because unless you find it absolutely abhorent then it's best left as is, remember it's only the 'odd' (word used correctly) browser warister whose ever going to see it in two different views anyway, the reason theure doing it in my mind discounts them as serious visitors.
If you don't want the addy made public but if you would like me to look at from a compatibility angle for you to see if it can be improved, send me a PM or email with your page address. I can assure you I will only look at it from a positive critique, but without being able to see the 'differences' it's really asking 'how long is a piece of string.
I'm no expert but I do dabble and build sites for friends and have a fair knowledge of PHP, Html, ASP and Java etc;

A little like yourself cyclic, I myself am at the moment dabbling in Web Design.
I am however learning from qualified teachers using a nationally recognised course guide. I am only at the beginners stage of things at the moment, and believe me I mean no offense, but one of the first things that an aspiring Web Designer should be aiming for is to make the page look the same no matter what browser is being used. Just my opinion but it does make sense considering that we are aiming at the biggest target audience possible.
Therefore vtlee my answer to your question would be to apply three different shell types and classes within your HTML markup.
The easiest way I have found is to apply three div classes- those being "ieshell", "mainshell", and "infoshell" directly after the opening body tag and closing(all three) directly before the closing body tag. I then link the following CSS to the HTML Doc-
.infoshell{
text-align:left;
padding:20px 40px 20px 40px;
}
.ieshell{
text-align:center;
}
.mainshell{
width:920px;
height: auto;
margin-left:auto;
margin-right:auto;
text-align:left;
This has worked for me in all cases. I have to say that I dont understand why you refer to different operating systems as this should have no impact on the way a Web page displays. As far as I know it is the browser and the way the HTML doc. and CSS are written.
Again cyclic- no disrespect- it does seem that even though we both are only dabbling at the moment you are more knowledgable than myself (PHP is my next subject- at the moment I AM only dabbling!)
Cheers guys and I hope this helps a bit vtlee
OMG- UPDATE- I just realised how late I am with this reply!!!! Anyway- hope it helps ummmm- some1